A Pakistani anti-narcotics court has sentenced a British mother of three to life in prison on charges of attempting to smuggle heroin to Britain.

Khadija Shah, a 26-year-old British national of Pakistani origin, was pregnant when she was arrested and gave birth to a baby girl, Malaika, while in prison.

The sentence passed by a court Tuesday in the city of Rawalpindi, near the capital means that Malaika, now one-year-old, would remain with her mother behind bars, according to her lawyer.

Attorney Shahzad Akbar said Shah was arrested at Islamabad Airport in 2012 for carrying 63 kilograms of heroin in two suitcases.

He said Shah was set up by a friend, whom he named as Imran Khan. He said Khan brought her along with her other two children, then aged 4 and 5, to Pakistan for a visit of several weeks, lavishly bearing all the expenses to gain her confidence.

''On her return to the UK, Khan gave her two suitcases for his friend whose daughter was getting married,'' said Akbar.

''She never knew heroin was concealed in the bridal clothes.''

Akbar said he will appeal the verdict.

''I am hopeful that I can get justice for her,'' he said.

The legal charity Reprieve has raised concerns over Shah's case.

''This is a terrible outcome for Khadija and her baby Malaika,'' said Maya Foa, a director of Reprieve.

The British government ''must ensure that Khadija gets the urgent assistance she needs to appeal her sentence so that her baby doesn't grow up behind bars,'' Foa said in a statement.

''As happens in hundreds of cases, she was used as a drugs mule without her knowledge, and yet is facing life in a Pakistani prison,'' Foa said.

The statement said Pakistan hands down ''excessively harsh sentences ... to vulnerable, exploited women such as Khadija.''

Due to its proximity to Afghanistan, where much of the world's opium is grown, Pakistan is a drug transit route. Authorities frequently announced the arrest of both Pakistanis and foreign nationals at airports. Drug cartels also used sea routes.